Use the following code for exporting crystal directly to pdf document.
Step 1: Create a Class Libray based project and create crystal report in the library. and compile it. (project dll file is created)
Step 2 : Create a simple asp.net web site and include the dll file of the above project.
Step 3:Use the following code, which uses the report and generates the pdf.
        CrystalReport1 c = new CrystalReport1();
        c.RecordSelectionFormula = "{Users.Username}='admin'";

        CrystalDecisions.Shared.DiskFileDestinationOptions  desoptions=new CrystalDecisions.Shared.DiskFileDestinationOptions ();
        desoptions.DiskFileName = Server.MapPath("a1.pdf");

        CrystalDecisions.Shared.ExportOptions exp=new CrystalDecisions.Shared.ExportOptions ();
        exp.ExportFormatType = CrystalDecisions.Shared.ExportFormatType.PortableDocFormat;
       
        exp.ExportDestinationType = CrystalDecisions.Shared.ExportDestinationType.DiskFile  ;
        exp.ExportDestinationOptions = desoptions;
        c.Export(exp);
        Response.Redirect("A1.pdf");